Question

Evaluate the sum of the following finite geometric series.

5+15+45 +135+ . . . + 1215
Sn=1

Answer 1

1820

Explanation:

The sum of the first n terms of a geometric series with common ratio r and first term a is:

a(1-r^n)/(1-r). Plugging this in 5(1-3^6)/(1-3)=1820